Isn't the spread between 5w40 and 15w40 wider at freezing?Of course a hot 15W-50 drains faster than cold 5W-40, did you read any of the responses in this thread? That isn't what you were asking about.
Here is a graph of the viscosity of a typical 15W-40 plotted against a typical 5W-40 (in Celsius). What do you see?
Again, no oil regardless of the winter rating is ever too thin in cold temperatures. If it isn't too thin when hot it won't be too thin when cold. In fact it will be massively thick.
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